This invention relates to a magazine for the automated changing of printing plates of a printing machine, especially a sheet-fed offset printing machine.
In sheet-fed offset printing machines, a printing plate is fastened on the plate cylinder by means of a clamping rail allocated to the leading edge of the printing plate and a clamping rail allocated to the trailing edge. The clamping rails are arranged in a groove of the plate cylinder. For changing a printing plate, the clamp at the trailing edge is first released and the printing plate is conveyed away from the plate cylinder by means of rotating the latter in a backward direction until the clamp at the leading edge can also be released. A new printing plate is positioned with its front edge in the leading edge clamping rail, the front edge is clamped and thereupon the plate cylinder is rotated in the forward direction until the other end of the printing plate can be inserted into and clamped by the trailing edge clamping rail. Tensioning of the printing plate is carried out via the trailing edge clamping rail.
In conventional printing machines, the above-described steps are carried out by the printer and are time-consuming. For shortening the set-up time, provision recently has been made of so-called fully automatic printing plate changing systems in which the previously used printing plate is taken from the plate cylinder into a magazine while the new printing plate is taken from the magazine to the plate cylinder. EP 0 530 577 A1 discloses a magazine for automatic printing plate changing. The magazine is used in a normal position as a guard in front of the printing unit and can be driven vertically and also pivoted about a horizontal axis. For service purposes, the magazine can be pushed into an uppermost position. For changing the printing plate, the magazine is first pushed a short distance upwardly and is then pivoted toward the plate cylinder. As a result, a gap is produced both above and below the magazine. The gap must be protected with additional guarding means for purposes of operational safety. In addition, the magazine pivots with its upper end in the space between the printing units. Accordingly, it must be ensured by means of further complicated protective measures that nobody can enter the space between the printing units or that no risk of injury exists as a result. There also exists a risk of injury in pivoting the magazine to the vertical position since the edges of magazine and printing unit interact like the parts of a shear. The accumulated multiplicity of necessary protective measures is very disadvantageous.
DE 3 940 796 C2 discloses a printing plate changing magazine which remains in the same location as a guard in front of the printing unit cylinders in the normal position and in the printing plate change position. In order to bring the magazine into an upper position for working on the cylinders, the magazine is articulated on two parallel rockers in the manner of a couple. This articulation is necessary since parts of the magazine running in a curve toward the plate cylinder in the lower region are also located underneath the plate cylinder. When the magazine is driven upwardly, there also is a horizontal movement in the region between the printing units. Complicated protective measures are also necessary here in order to prevent the possibility of injury to persons.
A semi-automatic printing plate changing device is incorporated in the printing plate drawing-in system PPL (Power Plate Loading) of the firm MAN Roland Druckmaschinen AG and is at present in use on the R 700. In this apparatus, demonstrated in the German magazine Druckwelt (Printing World) 4/25.02.1993, page 24 ff and also described in German Patent Application P 42 15 969, the printer need only remove a printing plate conveyed out from the plate cylinder through a slot in the sliding guard and to feed a new printing plate through the same slot to the plate cylinder. For this purpose, the sliding guard is pneumatically movable in front of the printing unit cylinders. A guiding apparatus is provided and is supported so that it can be pivoted into place on and removed from the plate cylinder. The guiding apparatus is designed as a sheet-metal profile extending over the format width of the printing plate and includes a feed-in rail integrally molded at its end. In the case of this apparatus, the printer grips the old printing plate conveyed out from the cylinder and draws it out of the opened leading edge clamping rail. The guiding apparatus is thereupon moved into operative position adjacent the plate cylinder, and the printer guides a new printing plate via the guiding apparatus into the leading edge clamping rail. By means of the feed-in rail of the guiding apparatus, the printing plate front edge is automatically threaded into the gripping region of the leading edge clamping rail. However, an old printing plate cannot be stored and a new printing plate cannot be made ready with this apparatus.
DE 4 214 207 C1 discloses a nip roll which can be put into operative position on the plate cylinder. An edge-bending strip extends parallel to the nip roll and also can be put into operative position on the cylinder. The nip roll is used in a known way to stretch the new printing plate under tension on the plate cylinder circumference. The edge-bending strip is used for bending the following printing plate edge around the trailing edge contour of the plate cylinder. This apparatus serves for drawing up printing plates already fed into the gripping region of a leading edge clamping rail on the plate cylinder but not for the feeding of a new printing plate to the plate cylinder.